The Soy Peptide Phe-Leu-Val Reduces TNF alpha-Induced Inflammatory Response and Insulin Resistance in Adipocytes

Abstract

Obesity-induced adipose inflammation plays a crucial role in the development of obesity-induced metabolic disorders such as insulin resistance and type 2 diabetes. In the presence of obesity, hypertrophic adipocytes release inflammatory mediators, including tumor necrosis factor-alpha (TNF alpha) and monocyte chemoattractant protein-1 (MCP-1), which enhance the recruitment and activation of macrophages, and in turn augment adipose inflammation. We demonstrate that the soy peptide Phe-Leu-Val (FLV) reduces inflammatory responses and insulin resistance in mature adipocytes. Specifically, the soy peptide FLV inhibits the release of inflammatory cytokines (TNF alpha, MCP-1, and IL-6) from both TNF alpha-stimulated adipocytes and cocultured adipocytes/macrophages. This inhibition is mediated by the inactivation of the inflammatory signaling molecules c-Jun N-terminal kinase (JNK) and I kappa B kinase (IKK), and the downregulation of I kappa B alpha in the adipocytes. In addition, soy peptide FLV enhances insulin responsiveness and increases glucose uptake in adipocytes. More importantly, we, for the first time, found that adipocytes express peptide transporter 2 (PepT2) protein, and the beneficial action of the soy peptide FLV was disrupted by the peptide transporter inhibitor GlySar. These findings suggest that soy peptide FLV is transported into adipocytes by PepT2 and then downregulates TNF alpha-induced inflammatory signaling, thereby increasing insulin responsiveness in the cells. The soy peptide FLV, therefore, has the potential to prevent obesity-induced adipose inflammation and insulin resistance.